The present application relates generally to marking machines for printing documents and the like onto sheets or other forms of media whose thickness varies between edges and, more particularly, to image and stacking orientation compensation methods and apparatus for use with media having marginal regions with different thicknesses such as, for example, DocuCard™ available from Xerox. The subject methods and apparatus are particularly well suited for use in commercial and office printing systems for marking copy sheets that have peelable labels or the like on one end thereof stacked in input and/or output trays whereby one marginal region of the stack will be thicker than the other marginal region. However, it is to be appreciated that the methods and apparatus described herein are applicable in a wide variety of other environments including, but not limited to, any marking or material handling system wherein orientation of the media relative to the system as it is processed therethrough is a significant parameter in the effectiveness thereof.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
In a high speed commercial printing machine of the foregoing type, large volumes of copy sheets are fed from storage to the transfer station of the printing machine where the toner powder image is transferred to the copy sheet. Frequently, the copy sheets are stored on a elevator type of sheet feeding tray. The tray is mounted on a frame and moves vertically from a sheet loading to a sheet feeding position. High capacity printing machines require large amounts of copy sheets. For example, a fully loaded tray may be loaded with several reams of paper with each ream containing approximately five hundred sheets. The sheet feeder advances successive uppermost copy sheets from the stack of copy sheets mounted on the tray.
Many conventional marking devices are configured to obtain optimized results with standard sizes of sheets of media such as, for example, letter sized media (8.5″ by 11″), A4 media, executive sized media, A5 media, legal sized media, envelopes, and the like. Specifically, for example, the media storage, media transport, and marking functions of these conventional marking devices are designed around these common media sizes such that these sizes of media can be most efficiently used within the devices. Accordingly, special steps and/or user-assisted functions may be required for uniquely sized media.
Some types of combined media for use in these conventional marking devices incorporate a smaller, uniquely sized, sheet of media fixed to at least a portion of a larger, standard sized, sheet of media. These types of media enable marking on the smaller, uniquely sized, sheet of media while utilizing the efficiently stored and transported, standard sized, sheet of media as a vehicle through the marking device. As a result, fewer special steps and/or user-assisted functions are required for marking on the smaller, uniquely sized, sheet of media.
Conventional marking devices that are optimized for standard sized media are designed to begin marking on a leading portion of the sheet of media as it is transported through the device. As a result, the smaller, uniquely sized, sheet of media is frequently fixed to the leading edge of the larger, standard sized, sheet of media. This allows for marking to begin on the leading portion of the combined media.
The above-described, conventional combined media, as result of having a smaller sheet of media fixed to a leading portion (in the vicinity of the leading edge of the combined media) of the larger sheet of media has a thicker leading portion than trailing portion (in the vicinity of the trailing edge of the combined media). Thus, the leading portion has a thickness equivalent to the thickness of both the small sheet and the large sheet while the trailing portion has a thickness equal to only the large sheet.
As used herein the term “leading edge” is intended to describe the edge of a sheet of media that leads the sheet of media as it is transported through a marking device. Similarly, the term “trailing edge” is intended to describe the edge of a sheet of media that leads the sheet of media as it is transported through a marking device. Similarly, the term “trailing edge” is intended to describe the edge of a sheet of media that is opposite the leading edge and trails the sheet of media as it is transported through the marking device. As used herein, the terms “feeder” or “media feed mechanism” are intended to describe devices that feed unmarked media into a marking device. The terms “stacker” or “media stacking mechanism” are intended to describe devices that stack marked media after being marked by the marking device. It should be appreciated that the feeder and/or stacker may be included in the marking device or may be separate devices attached to the marking device.
One example of the above-described combined, multi-thickness, media is Xerox Corporation's DocuCard® media. For ease of explanation, the following exemplary systems, method and, programs will be disclosed using DocuCard® type media as an example of combined, multi-thickness, media; however, it should be appreciated that the principles disclosed herein may be applied to any type of media with each sheet having at least two different thicknesses.
Conventional media feeding mechanisms are designed such that feeding reliability is generally maximized when the top of the media stack is level front to back and side to side.
Conventionally, however, the above-described combined, multi-thickness, media is packaged and loaded into the feeder of marking devices with each sheet having the same orientation. Because each sheet has a same orientation, the marking device may process each sheet in the same manner, thus simplifying the marking process. Due to the orientation of the sheets, the thicker portion of each sheet of the combined media is oriented above the thicker portion of the sheets below it and the thinner portion of each sheet of the combined media is oriented above the thinner portion of the sheets below it.
As a result, and as described in further detail below, when the combined multi-thickness media is stacked and loaded into a marking device, there exists a substantial difference in thickness between a leading edge portion of a stack corresponding to the thick portion of the media and a trailing edge of the stack corresponding to the thin portion of the media.
This difference in thickness in the stack of media may cause problems when feeding and transporting the media through the marking device. Because of an increasing angle of incidence of the lead edge of the sheets to the feed mechanism, tall stacks of the combined multi-thickness media may not feed at all (misfeed), or may feed two or more sheets of media simultaneously resulting in a jam.
Currently, in order to avoid jams or misfeeds in conventional general purpose marking devices, user must limit the number of sheets of multi-thickness media that are loaded into a media tray in order to reduce the overall thickness difference between a leading edge portion of the stack and the trailing edge portion of the stack.
Similarly, the performance of conventional media stackers is substantially degraded when the marked media being stacked is not uniformly flat. As media is stacked sheet by sheet in the stacker of the marking device, the top of the stack becomes increasingly unlevel until the slope is great enough that the down-slope gravitational pull on the sheet exceeds the friction between sheets, and the sheets start to slip off of the stack.
Currently, the stacker must be unloaded more frequently, at lower than maximum possible stack height in order to avoid sheets from falling off the stack.
Various approaches have been devised for leveling sheets. In one example, U.S. Pat. No. 4,942,435 discloses a leveling supporting means for use in an electrostatographic machine for supporting a stack of sheets that is adapted to be interposed between a tray and a stack of copy sheets when one marginal region of the stack has a greater thickness than the other marginal region. The supporting means includes means for fixedly supporting the other marginal region of the stack of sheets and means for resiliently supporting at least the one marginal region of the stack of sheets having the greater thickness.
U.S. Pat. No. 5,364,087 discloses a tilting tray for feeding and stacking specialized forms. A modular tray is insertable into a printing machine which is arranged to have a stack of copy sheets disposed thereon. When one marginal region of the stack of copy sheets has a greater thickness than the other marginal region, the sheets are supported such that at least the opposed marginal regions of the uppermost sheet of the stack of copy sheets are at substantially about the same level while that portion of a majority of the copy sheets with the thicker marginal regions is downwardly supported at an acute angle with respect to the surface of the uppermost copy sheet in the stack.
In view of at least the foregoing, it is beneficial to provide systems, methods, and programs that allow for a large number of sheets of combined multi-thickness media to be loaded in the feeder of a general purpose marking device and stacked in the stacker of a general purpose marking device, without substantial expense and hardware modification.